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Driving force of a model car - equation not working

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  • 14-02-2015 7:41pm
    #1
    kapisko1PL
    Registered Users Posts: 277 ✭✭


    Hey guys,

    I need to ask you for little help. It is to do with a project of a small battery powered car. I must be doing something wrong because the equation i have been provided with for this project doesn't seem to work (I am doing something wrong; yes I know).

    First of all; is the driving force of the car force that is available at the driving axle of the car or is it the spare force that will cause acceleration?

    Second thing:

    My model car weighs 11N; assuming static friction coefficient of 0.4 then -> (11)(0.4) = 4.4N static friction force.

    From my equation: Fd=(2Tm*Da)/Dm*Dw; where:

    Fd = driving force
    Tm = torque = 37.5mNm (given)
    Da = diameter of axle pulley (10mm)
    Dm = Diamter of Motor Pulley (20mm)
    Dw = Diameter of the wheel (56mm)

    From the above values using this equation I get a value for a driving force of 0.669N which is way to small to even move the car a little bit.

    Another question:

    if the output speed of my motor is 330RPM will the RPM double on the axle provided the diameter of the axle pulley is twice the value of the motor pulley? i.e. 660RPM? Will the same happen to torque? (i.e. be twice as small but there will be more power?


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